Basinc MongoDB commands
Commmand |
Description |
Example |
mongod |
start the mongo service |
mongod --dbpath /home/mongo --logpath /home/mongo/mongod.log --bind_ip 0.0.0.0 |
mongosh |
command run mongodb shell |
mongosh |
show dbs |
list databases |
show dbs |
use db_name |
Switch to database db |
use company |
db |
show current database name |
db |
show collections |
List current database collections |
show collections |
Insert
syntax |
Description |
Example |
insertOne (data, options) |
insert one document |
db.people.insertOne({ "ssn":1, "name":"Ali","age":20}) |
insertMany([{document1},{document2}]) |
insert many documents, square brackets are mandatory |
"db.sales.insertMany([ { ""item"": ""abc"", ""price"": 10}, { ""item"": ""xyz"", ""price"": 5 } ])" |
Delete
syntax |
Description |
Example |
deleteOne(filter, options) |
delete the first matching document from collection |
db.project.deleteOne( { "pnumber": 1 } ) |
deleteMany(filter, options) |
delete all matching documents from the project collection |
db.project.deleteMany( { "plocation": "Stafford" } ) |
Update
syntax |
Description |
Example |
updateOne(filter, data, options) |
update one document |
db.sales.updateOne({"item":"abc"}, { "$set" : {"price": 22} } ) |
updateMany(filter, data, options) |
update matching documents. |
db.sales.updateMany ( { ""_id"":{""$gte"":14, ""$lte"":16} } , { $unset : { ""price"" : "" ""} } ) |
$set to update the field value
$unset will remove the field
Index
syntax |
Description |
Example |
createIndex( {keys} , {options} ) |
Creates indexes on collections. |
db.project.createIndex( { "pnumber": 1, "Pname": -1 } , { "name": "pno_name" , "unique": true} ) |
dropIndex(index) |
Delete index |
db.project.dropIndex("pno_name") |
getIndexes() |
List indexes on collection. |
db.project.getIndexes() |
if index name was not specified withing options, the name will be generated automatically.
1 = ascending order
-1 = descending order
Find
syntax |
Description |
Example |
findOne(filter, options) |
find first matching document |
db.employee.findOne({"dno": 8},{"_id":0,"fname":1,"lname":1}) |
find(filter, options) |
find all matching documents |
db.employee.find({"dno": 8},{"_id":0,"fname":1,"lname":1}) |
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Query methods
syntax |
Description |
Example |
sort({field_name:1 or -1}) |
find first matching document |
db.sales.find().sort({"price": 1}) |
limit(n) |
Limits the number of documents |
db.sales.find().limit(3) |
skip(n) |
Skips over the specified number of documents |
db.sales.find().skip(3) |
1 = ascending order
-1 = descending order
Aggregation Pipeline
syntax |
Description |
Example |
$group |
The $group stage separates documents into groups according to a "group key". The output is one document for each unique group key. |
db.employee.aggregate([ { "$group" : { "_id" : null, "averageSalary": { "$avg": "$salary" } } } ]) |
Accumulator Operator |
| |
$avg |
Returns an average of numerical values. |
| |
$max |
Returns the highest expression value for each group. |
| |
$min |
Returns the lowest expression value for each group. |
| |
$sum |
Returns a sum of numerical values. Ignores non-numeric values. |
$lookup |
Performs a left outer join to a collection in the same database to filter in documents from the "joined" collection for processing. The $lookup stage adds a new array field to each input document. The new array field contains the matching documents from the "joined" collection. The $lookup stage passes these reshaped documents to the next stage. |
db.orders.aggregate( [ { $lookup: { from: "inventory", localField: "item", foreignField: "sku", as: "inventory_docs" } } ] ) |
The $lookup takes a document with these fields: |
| |
from |
Specifies the collection in the same database to perform the join with. |
| |
localField |
Specifies the field from the documents input to the $lookup stage. |
| |
foreignField |
Specifies the field from the documents in the from collection. |
| |
as |
Specifies the name of the new array field to add to the input documents. |
Logical operators
$and:[array] |
AND operation between all array of expressions |
$or:[array] |
OR operation between all array of expressions |
$nor:[array] |
All array expressions must fail. |
$not:Expr |
Performs a logical NOT operation on the specified <operator-expression> |
Comparison operators
syntax |
Description |
$eq |
Matches values that are equal to a specified value. |
$ne |
Matches all values that are not equal to a specified value. |
$gt |
Matches values that are greater than a specified value. |
$gte |
Matches values that are greater than or equal to a specified value. |
$lt |
Matches values that are less than a specified value. |
$lte |
Matches values that are less than or equal to a specified value. |
$in |
Matches any of the values specified in an array |
$nin |
Matches none of the values specified in an array. |
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